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Why do modern jetliners provide Thrust Reversers at all in their design decisions?
Let's start with the following knowns (please correct me if I am wrong about any):

The braking force provided by the wheel brakes is much larger than that by the thrust reversers
One is not allowed to does not take credit for reversers when calculating landing distance in most aircraft. (A few exceptions exist)
Thrust reversers add quite significantly to the weight and complexity of engines
An improperly deployed thrust reverser can be critically dangerous and hence many redundant systems must be provided to prevent unwanted deployment
Modern civillian aircraft never rely on reverse thrust during flight
In the history of aviation incidents quite a few have been related to reverser problems or procedure errors.

In the light of this why aren't more large civilian aircraft designed that use only wheel brakes + spoilers to do all their braking?
More specifically, suppose you had to re-assign the braking force provided by the reversers in the initial rollout to spoliers alone how much more spoiler area would one need to provide?
Overall, spoilers + wheelbrakes seem far more docile and benign than the complexity and risks associated with reverse thrust?
What gives?
PS.
Are the any modern large passenger jet aircraft that don't have reversers at all?

Your point #2 is incorrect. The Next Gen 737 performance data DOES take credit for reverse thrust on landing.  Adjustments are applied if a TR is inoperative.

@RalphJ is right, your point 2 is not correct in all cases. Can you cite that or be more specific?

I'll correct my #2. I'm open to corrections. Thanks.

There are  a couple of reason for the presence of thrust reversers:

To reduce wear on the brakes.

To provide a margin of safety (for example in wet conditions).

In 1995, NASA carried out a survey on airlines Why Do Airlines Want and Use Thrust Reversers?. The results of the survey, though dated, give an indication of presence of thrust reversers.

The main reasons given by the airlines was to provide additional stopping force in adverse weather and to reduce brake wear.

The first question posed to the airlines was "why do we have thrust reversers?" (...) The number one reason given by the airlines was to provide additional stopping forces in adverse weather conditions (i.e. on wet, slushy or slippery runways). The airlines also use thrust reversers to reduce brake wear and to provide directional control and additional safety margins during an aborted takeoff (RTO).

According to the airlines, the thrust reversers were there because they wanted them there. This meshes with the fact that the thrust reversers are not used in calculating stopping distances during certification.

When the airlines were asked who they perceived as the principal organization behind the installation of thrust reversers on commercial transport aircraft, the airlines responded that they were. That is, the
aircraft manufacturers put the systems on board the airplanes because the
airlines want them.

Most airlines recommend using the thrust reversers early in the landing to minimize braking.

The airlines weigh the economic benefits of using the thrust reversers (and engine wear) against the use of brakes and the results seem to indicate a significant amount of money saved by using thrust reversers. The report notes:

... the savings in brake system costs due to the use of thrust reversers was estimated. The results show that the total yearly savings in brake system costs is about \$8.6 million, or an average of about $17,700 per airplane for airline 17.

Though this is almost certainly an exaggeration, the numbers indicate that the airlines would definitely prefer thrust reversers over increased braking.
In the end, the reverse thrust can be important in reducing the runway requirements in case of a wet runway. In 1999, a Qantas 747 overran the (wet) runway in Bangkok and landed up in a golf course. Qantas has used only idle reverse thrust rather than full power during the landing as per the operational procedure. The official accident report included data from Boeing 747-400 Flight Crew Training Manual, which stated that,

Immediate initiation of reverse thrust at main gear touchdown and full reverse thrust reduce brake usage, thus minimising brake temperatures.
To minimise wear of carbon brakes, minimise the number of brake applications. Use maximum reverse thrust and operate the autobrakes normally.
The importance of establishing the desired reverse thrust level as soon as possible after touchdown to minimise brake temperatures, tyre and brake wear, and to reduce stopping distance on very slippery runways cannot be overemphasised..

As a result, Qantas revised their operational procedures, requiring full reverse thrust. Brake wear is an important reason for having thrust reversers. For example, in Airbus A380:

... unlike the thrust reversers on most airliners, including the Boeing 747 jumbo, they do not stop the aircraft in a shorter distance than brakes and spoilers alone. They do, however, take some of the strain off the brakes and are useful if water or snow makes the runway slippery.

The BAe 146 lacks a thrust reverser; it makes do with an airbrake in the tail and spoilers all along the wing for braking (which should give an indication of how much spoilers is required to eliminate reversers). The 146 got away with that because of the low touchdown speeds (~90 kt) and the huge airbrake, which is not avialble in the other commercial airliners. For the same amount of spoiler area in other commercial airliners (in absence of airbrakes), they (spoilers) would occupy most of the wing surface, increasing weight and complexity. Some Embraer ERJ 145s also lack thrust reversers (they are optional).

The added complexity is a valid point. However, the additional braking option provides enough benefits to offset the added cost. Also, it is not accurate that credit is never given for reverse thrust. Per 14 CFR §25.109, when calculating accelerate-stop distance, reverse thrust is not considered for a dry runway, but:

May be included as an additional means of deceleration using recommended reverse thrust procedures when determining the accelerate-stop distance on a wet runway

So at least from an FAA certification standpoint, reverse thrust is considered as a benefit in wet conditions, which is generally the more critical case.
Yes, the wheel brakes provide the majority of the braking force. But that is also a function of your second point. Credit is not always allowed for the reversers, so that means their use merely reduces stopping distance. It is often preferable from an operations standpoint to not use up the entire runway when landing. Exiting the runway earlier can reduce delays and taxi time, and makes room for the next aircraft in line for that runway. If a longer landing roll is still acceptable, the thrust reversers help to reduce the strain on the brakes. While modern brakes are much improved over older designs, they are still an item that needs replacing after use. Harder braking also results in higher brake temperatures, which may require extra time for the brakes to cool.
It's helpful to have an extra layer of safety in landing distance calculations. If you calculate landing distance that is just within the available distance, there are still many failures that can prevent the aircraft from stopping. The thrust reversers offer additional braking force that can offset unplanned deficiencies in other areas.
Other options for providing braking force have their own problems. For an example, look at the spoilers on the 737 NG. You can see that they already occupy all of the available spanwise area. That means the chordwise area would need to be increased. This would also increase weight and complexity. Additional panel area would be needed, and the supporting systems would need to be reinforced. Also, while thrust reversers offer some amount of braking force at any speed, the effect from spoilers drops off more significantly at slower speeds.

Thanks. But what about adding enough spoiler performance to compensate and thus remove the thrust reversers from the equation entirely? Is that not a feasible design option?

Also, I am not arguing for increasing the landing distances. Just wondering if the current best landing distance performance can be more cheaply / safely provided using wheel brakes and spoilers alone.

Of note is the NASA study cited in @aeroalias's answer, which includes a graph showing that, for an average aircraft, coming to a stop on an icy runway takes almost three times as much runway without reversers as it takes with them.

@curious_cat: An airplane has a lot more mass than all of the air it's going to pass through while decelerating after touchdown, and a plane at flight speed will have a lot of momentum it needs to transfer somewhere.  The only options to accomplish that are to either transfer that momentum to the ground, or accelerate a lot of air to a speed much faster than the plane.  Aerodynamic means can do a lot to improve wheel traction, but then comes a second problem: an airplane will also have a lot of kinetic energy which is going to have to get converted to heat "somewhere".

@curious_cat: Even if wheels have perfect traction, brakes are going to wear down a fair amount if they have to absorb all of the kinetic energy of a landing airplane.  If one can transfer the kinetic energy of the plane into air that's coming out of the thrust reversers, that kinetic energy can be dissipated when that air mixes with stationary air nearby.


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Why does Logan Airport's Runway 32/14 only have arrivals on the 32 heading?
I was going through this PDF document on Logan International Airport's runway usage and I saw that Runway 32/14 only has arrival activity. Why is that the case? Is this the the reason or part of it why there are only stripe marks on the side of the runway close to "32"?

https://en.wikipedia.org/wiki/Logan_International_Airport#Runway_14.2F32

Related, and also this one. Possibly a dupe (depending how you look at it).

(Much of my answer below will be drawn from "The 30-year saga of 14/32", a 2006 Boston Globe article which is unfortunately subscription-only but which I have access to via an institutional database.)
Runway 14/32 has been a long-standing bone of contention at Boston Logan.  Like many urban airports, Boston Logan is constrained by the fact that there are many people living nearby who don't particularly like jets flying low over their houses, and who are willing to organize in opposition of any increase in operations at the airport.   Massport, the organization in charge of Boston Logan, had originally proposed to build a new runway in the late '60s.  This met fierce opposition from community members in East Boston who were opposed to additional take-offs and landings over their homes.

[I]t's taken no less than 33 years for 14/32 to become reality, a testament to how politically charged Logan expansion has been ever since demonstrations in the 1960s, when East Boston mothers lay in the streets to protest the destruction of Eastie parks and homes.  ...

The Hyatt Harborside Hotel (now the Hyatt Regency Boston Harbor) was built in the 90s to act as an impediment to runway expansion:

In the 1990s ... Frederick P. Salvucci engineered construction of the 270-room Hyatt Harborside Hotel, a stone's throw from the end of the new runway, largely to create as big an obstacle as possible to Massport extending 14/32 or using it for planes flying over the city.

In the end, Boston Logan was barred by court order from allowing takeoffs from 32 or landings on 14, except in emergency:

By court order, use of 14/32 will be restricted to planes taking off and landing over Boston Harbor, so Massport will be legally forbidden - except in emergencies - from using the runway to let planes take off or land over South Boston and downtown.

This still allows for three runways to be operative when winds are from the northwest or southeast (along with 15L/R or 33L/R), so the hope was that even this "half-runway" would result in fewer delays at BOS during bad weather.  Whether or not this has panned out to be true in the decade since, I do not know.

A quick look at Google Maps shows a large building to the north west of the runway which would make arrival to 14 or departure from 32 hazardous.

@ymb1 the building is the one mentioned on Wikipedia as being intentionally placed to block the runway on that end, and the obstruction note is followed by APPROACHES TO RWY 14 NOT AUTHORIZED.

@fooot Indeed.  The local authorities chose the spot carefully to ensure that the runway could not be extended.

@ymb1 the obstacle is less than a 737's wingspan off centreline. The slope from the runway threshold to the roof exceeds 7 degrees. By what measure do you come to the conclusion that it's no issue? May I suggest you to ask some questions on runway protection zones?

@ymb1 -- A380 no -- but 737s operate in and out of KEYW which is 4800' (albeit with a payload restriction)

I'm sorry, but I'm confused; is the building why there are no normal  landings on 14, or was it build to prevent landings there. OK, my own sentence confused me now. Which came first, no landing, or the building?

Landings on RWY 14 and takeoffs on RWY 32 at KBOS are prohibited according to the A/FD, most likely for the obstacle clearing reasons stated above.

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What is "linear holding"?
In a Lisbon RNAV procedure, the LOST COMM box mentions "LINEAR HOLDING".
What are the purpose of this instruction during approaches?

Linear holding (LH) is a holding technique consisting in extending an arrival route instead of flying a racetrack pattern. Currently the LH flavor deployed, including for Lisbon arrivals, is a flexible vectoring, the point merge system (PMS):

Source.
In the normal case, the aircraft is directed to the merge point, a point on the route ahead, usually a fix from the approach procedure. When the aircraft needs to be delayed, it starts flying an additional arc of circle centered on the merge point. When the spacing with the previous aircraft is adequate, direct navigation to the merge point is resumed:

Source, modified.
The number of entry points can be varied, 1, 2 like above, or more. Aircraft flying different arc lengths for spacing requirements:

Source: Youtube, Ethiopan ATCA.
From SKYbrary:

Linear holding can be designed into an RNAV STAR. It allows ATC to delay, sequence, and integrate aircraft arrivals by giving routings along predeﬁned variable legs to speciﬁc points, instead of providing radar headings. It can also entirely replace or signiﬁcantly reduce the need for traditional holding stacks.

‘Point Merge’, shown below, is a particular type of linear hold that is already in operational use at some airports. ATC arrival clearance is given for the complete longest linear hold route. As the correct spacing is achieved, the aircraft is instructed to route to the ‘merge point’ from where a single arrival path is resumed.

LH (PMS flavor) is already implemented at several terminal areas in Europe and Eastern countries, to optimize the management of their dense and growing traffic:

Source.
LH is useful for performance based navigation (PBN) and continuous descent (CDA). The flow is more predictable. It contributes to reducing the total flight time, noise and fuel consumption. LH is used for small corrections in the sequencing (e.g. up to 5 minutes). Longer delays required by metered traffic (e.g. AMAN) is still based on racetracks or equivalent, prior to the LH.
This is also described in Portugal AIP, for arrivals at Lisbon:

ARRIVAL ROUTES LPPT RNAV Arrival Routes are based on the Point Merge System (PMS), a systematized method for sequencing arrival flows by merging inbound flows to a single point. All Point Merge Systems require a level segment on the PMS arc which may be considered as a linear hold. This means the linear hold will resemble an arc with the Merge Point (MP), at the centre of the arc.

While an aircraft is on the linear hold, it can be instructed by the controller to fly “Direct To” the MP, at any appropriate time, to shorten the trajectory rather than flying the entire PMS Arc. For each RWY there are two linear holding entry points: RWY02: MAZUK and ORTUG RWY20: EKLID and DEKKI. The MP for each RWY is coincident with the IF of the Instrument Approach Procedures RWY02/20.

More:

Point Merge implementation: A quick guide
New ATC procedures, unintended eﬀects on the ﬂight deck?
PMS from ATC side, 4 entry points on one runway, Youtube.

What a peculiar name for a pattern that consists of circling, arcs and a sector, but nothing linear

nicely put @Jpe61 !@

@Jpe61 The time on the arc allows to scale your time on the pattern linearly, unlike time (rounds) spent on a racetrack that has only discrete values

@Bergi ah, I see, derived from linear algebra then? Still a bit far fetched imo. Guess they had to find a term that would not be confused with something already used such as "arc", "continuous", "vector(ed)" etc.

@Jpe61 Just a guess. I have no idea about aviation.

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Can Flight Simulators (FSX P3D) give you the expecience you need to fly a RW plane?
So I am flying on the sim for about 7 years now, which 3 years on the (PMDG) 777 and 737NG. Flying on the sims is almost like the real world right now, you can download multiple addons (PMDG, Aerosoft for planes ORBX for scenery, REX and ACSC for weather, etc, etc), download checklists, join online networks (IVAO, VATSIM) and so on. But can step into a 737NG right now and fly it with my sim experience?
What are the real differences between the sim and real world if it's about flying. And if I would step into a 737 now, what challenges can I expect during flight, which I probably didn't encounter during my flights in the simulator.
Consider this:

I fly 7 years on the sim
3 years on the PMDG 737 and PMDG 777
Flown with multiple failures (Engine Fire, ADIRU failing, etc, etc)

Thanks in advance!

Related: Can Microsoft Flight Simulator help me learn to fly (or make me a better pilot)?

@RonBeyer I know, but isn't answering my question

If you are just flying a standard desktop rig, you probably will have a hard time locating and actually finding the actual buttons and switches on the real thing.

@HugoWoesthuis I know, that's why I said it was related, not a duplicate :)

OP says the 'related' link doesn't answer his question, though the accepted answer here is basically a summarization of the other post.

@SMSvonderTann In the 737, I know also where the knobs are and more important: what they do ;).

I'm a real world pilot, I've flown the PMDGs a lot and I've also flown a full size simulator. So I know all the systems and the switches/controls.  But there are many things missing.  E.g. did you know that on the 737-400 (and I assume other Boeings), you must lift the speed brake lever before you can deploy it or move it to the armed gate?  The other question is a duplicate since the answers within it also answer this question.  The main problems are that you do not get feedback for your ears (movement) and eyes (peripheral vision) from PMDG.

@SMSvonderTann You should check out the PDMG 777.  With the exception of "minor" systems like the ACARS, everything is modelled very accurately.  I know where every control is.

Don't people usually a) use a desktop simulator, and then b) use a free standing approved simulator that surrounds the pilot and has realistic controls, and then c) get checked out by an instructor in the plane itself, and then d) spend some number of hours with a seasoned pilot as a copilot before they're approved to fly something with a lot of passengers?

I would expect the challenges to be related to 1) being used to where the actual controls are and how they feel, 2) being used to how it all feels in actual flight, and 3) the impact that actual flight and actual responsibility has on your mental state. I guess what you want to know, though, is what specific, substantial differences exist, if any, between the particular simulator you're using and the real thing. I guess only someone with experience with both would be able to answer that.

GdD brings up some good points but that really depends on what you mean by "home simulator" and it depends on the airplane. There are some people that have taken it to the extreme and built simulators that are fairly close to real and provide a solid learning platform not only for the flying but the actual physical operation of the controls. You can fairly easily build a home sim for a small plane that has all the controls and instruments you would see in a real plane and even in emergency situations you will see real warning lights in your sim and be able to mitigate it as you would in a real plane (nothing is stopping you from wiring in a smoke machine either).
As for the flight dynamics they get more real as time goes on and computers get better and better. I use X-Plane and simulate the Piper Archer I fly in real life which I find to be pretty close to the real thing from a flight dynamics/response stand point. My simulator did a great deal for my cross wind proficiency when I was training. I cant say I learned to fly in the sim but I did a great deal of honing of my skills in my home sim.

The sim is a tool not a replacement

If you understand this you will better be able to realize that the sim can provide you a great deal of proficiency and can suffice for training in some (not all) cases. Even the big guys use simulation to train for the real thing (this article provides some nice pros and cons). The FAA even considers approved simulator time to count towards certain things.
Unless you have a full motion sim at home, the sim wont provide you with the feeling of flying which is very hard to replicate. It wont disorient you in IMC by having G-Forces cause your vestibular sense to distrust the instruments. It wont physically throw you around on a bad cross wind landing with wind sheer causing your knee to bump the yoke. It wont shake you to the point you drop your iPad while briefing an approach plate. It wont spin you until your lunch decides it wants to be elsewhere. These are the kinds of experiences you may only find in a real plane...
One last thing to consider as well is some what of the reverse case. Aircraft cockpits are actually getting closer to computer based units as time moves on. Its common to see keyboards in airbus cockpits and many of the former steam gauges have been all but replaced with screens. As we move into a more automated era some switches have even been lost to digital control units. Even the flight controls them selves have moved into the modern age with fly-by-wire systems removing physical linkage from the side stick to the control surfaces.

A home-based simulator is not enough to safely fly a plane in the real world.  You can learn a lot from a desktop simulator, however it doesn't give you enough of the right kind of experience. A computer joystick won't feel like the real thing, the inputs you put in won't be the same and these things are important. When you take off the first time you need to know how far back the stick needs to go. Only the real thing or an approved simulator gives that kind of experience.
In an emergency you need to know by instinct where every switch and knob is, you can't afford to be hunting around for the APU controls!
Most importantly you won't learn anything about Cockpit Resource Management (CRM, also known as Crew Resource Management), that is how to be a part of a functional and safe crew. Commercial airplanes are almost all multi-crew, and all pilots are taught how to operate in a standard way. A desktop simulator is not going to give you any of that experience.

Depends.  Could you actually fly a 737 to save your skin?  Maybe.  Are you ready to enter the airlines as a 737NG FO or captain on a revenue carrying flight?  No.
As they say, there is nothing new under the sun and successful flights and landings of aircraft by neophytes without formal training have happened in the past.  When I was in high school, I landed an F-4G at KBOI at night in an Air National Guard simulator out at Gowen Field.  There is also the story of an USAF mechanic named George Johnson, who soloed in an F-86 at night after only two hours of dual instruction in a Piper Cub.  Then, there was this Belgain TV host who landed a real 737 with only a month worth of flight training.

However bear in mind that all these exampled given above are flukes and were also done, either planned or unplanned, under the direct supervision of instructor pilots and other staff to guide them in.
Now I will comment that there are a number of payware houses who manufacture with a reputation for super realistic flight models e.g. PDMG, VRS, RealAir quickly come to mind on that.  And modern simulators like FSX, P3D and X-Plane are pretty realistic with good flight dynamics, accurate weather effects, relatively realistic airspace use and ATC, etc.
But it is still inadequate to qualify you as a captain or FO on a B737 for a variety of reasons.

Kinesthetics:  It is one thing to 'fly' a realistic game with a joystick, another thing entirely to have your fanny strapped into the real thing and intuitively operate it correctly.  For the first few flights, it's going to feel totally different from your simming experience.  You are not yet proficient at 'brain stem flying' in the real thing from your experience in the sim.  Everything you think you know about flying has just gone out the window and you only have about 10% of it at your disposal.  You are acutely aware of turbulence, bumps, acceleration and deceleration from throttle inputs, maneuvering, etc.  And things happen very fast in a terminal environment when moving at 200 KIAS while having to deal with airmanship, navigation, communication, frequencies, several hundred aircraft system, weather, flying instrument approaches, etc.  It is most likely to seriously overload a newcomer who is expected to do it in a professional manner.
Flight dynamics:  As mentioned above, these sims and payware a/c are pretty accurate but do have their limitations.  FSX, for instance does not model jet engine or turborop engine performance/response and edge of the envelope flight accurately (the core of the game originally designed for single engine pistons, I believe), so there are going to be differences in handling and feel between the game and the real thing.
Avionics:  These are replicated in sim games ranging from pretty darn good (e.g. Reality XP's GNS430/530) to horrible (default FSX).  I don't know how PMDG does as far as it's ability to replicate a 737's avionics suite, but there are going to be differences between the sim and the real thing ranging from the very benign differences in a non critical submode somewhere to major functional differences e.g. the AFCS, AT, approach modes, etc. which can have disastrous consequences in a real airplane if they are operated incorrectly.  Also avionics configurations are going to vary from airline to airline, airplane to airplane, adding additional complications.  You would have to consult with the approved airplane flight manuals in each a/c for specifics here.
Real world flying abilities - If all your flying experience is on a sim game, chances are you're doing something wrong.  Sims can teach you a lot but they are simply not a substitute for FAA approved flight instruction.
Weather - Weather in sims flat out sucks.  Sure it can simulate clouds, fog, rain, etc. but it does not simulate a lot of the dangerous stuff well.  You can take off directly into a severe thunderstorm or microburst in FSX without the slightest bump.  Do that in real life and you're likely to star in your own NTSB report.  Sims also don't simulate a lot of the unpredictability associated with weather where one minute you're flying in benign clouds and the next you're inadvertently in moderate or severe icing conditions, severe updrafts/downdrafts when operating at an airport surrounded by mountains, etc.  There are a lot of dangerous weather phenomena specific to certain regions of the globe which are not modeled well in these sims and would be well known to local flyers.
Flight operations and ATC - dealing with sim ATC is kind of like having a conversation with a talking Barbie doll; sure, it says all the right things in the right order but it's never the same as a dynamic conversation with a real human.  In the real world, controllers may be a lot more dynamic and may deviate considerably from ideal protocol in a textbook.  They can have additional instructions for taxiing, traffic separation, sequencing for approached, preferred traffic maneuvering to relieve congestion and expedite operations.  For instance in a sim you can contact Los Angeles approach and request the ILS RWY 24R into LAX;  In real life, LA approach is going to laugh at you and then give you the option of flying either the ILS for RWY 24L or RWY 25R, as 24R is being used for departures and would interfere with their schedule.
Unpredictability of real life - It's said that Murphy's Law puts in lots of overtime and this can be especially true of flying.  The environment constantly changes and you have to be ready to adapt to it.  For example, watch this radar track of airliners approaching and landing at KATL as a series of severe thunderstorms develop over Atlanta area one afternoon.

  Unpredictability can vary greatly from traffic congestion, to having to hold on the ground to wait for a gate due to local airport computer problems all the way up to serious emergencies like structural failures, decompression, diverts because a passenger had a heart attack and needs medical attention, etc.  This just can't be replicated in a computer game.
Graver consequences of emergencies - You're flying at FL370 when an explosive decompression occurs.  You have 5 seconds to react properly to this or you and everyone on board will lose consciousness and die.  No computer game can prepare you for that kind of an experience.  It's a looonnnggg way down to terra firma and you're going to have to get a crippled airplane back down there safely all while dealing with the emergency and fighting that visceral reaction in the pit of your stomach that this is no joke and your life is really in danger here.  In the sim?  OK, so the aircraft broke up from being overstressed.  Push reset and try again.

To develop the kind of professionalism needed to do this, you're going to need time and experience flying the real thing.  It's the reason the FAA requires you have logged at least 1500 flight hours in the category and class of aircraft to be used to become an ATP captain and sets at least 250 flight hours as a minimum requirement for other kinds of commercial flight operations.  You will need this experience - this seasoning - if you will to become proficient in these kinds of conditions and situations and complete the flight successfully.

This is an anecdotal answer, so I'm sorry if it doesn't really fit the site but in my opinion, there's one thing that no simulator, no matter how good, can prepare you for: The emotions you'll feel.
No matter how realistic the graphics are, no matter whether it's got full motion capability and no matter how good the flight model is - until you've taken on that responsibility you just won't know how well you're going to commit.
Like many people here, I spent a lot of my time in flight simulators - afterall, they're a lot cheaper than the real thing. But, never once, have I broken into a cold sweat. Never once have I had one of those moments where I just wanted to be on the ground, having completely utterly forgotten everything I've ever learned.
People focus on a lot of the technicalities, but the truth is I've always felt pretty at home in a cockpit. Moving away from big planes, your average GA plane is not hard to get off the ground- checklists are easily memorized and for the most part you can fly just fine without touching too much. And, I suspect if you've got enough sim experience you could conceivably pull off a circuit - the real, question though, is when you're sat there all by yourself at 1000', sweating, are you going to have the confidence in yourself to fly that plane back down to the ground knowing full well if you screw it up you may not be going home. And what about a stall - when you're sat there, and it's all on you are you going to have that confidence to point the nose down when all you want to do is go up! And, back to the big toys, maybe you're about to kill several hundred people.

As far as anecdotes go, actually, on my own first real-world stall exercise I ended up pushing the nose too far down! Good thing we were at somehing like 2000-2500 feet AGL. The second attempt was much smoother. So you can do it wrong both ways.

@MichaelKjörling I suppose I was thinking more about stretching the glide at low level - I think we all have that desire to pull back once the ground starts getting closer a little sooner than we'd like! But yes, absolutely - either way there's little substitute for being sat in the seat!

"I think we all have that desire to pull back once the ground starts getting closer a little sooner than we'd like!" Indeed! I don't know how many times I've either been at the brink of making that mistake, or actually made it... thankfully without needing to star in my own accident investigation report so far! I think that's what instructors are for.

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How are light gun signals handled at remotely controlled airports?
In a comment @randomhead mentioned:

Remote towers are already in use at several sites in multiple countries. Off the top of my head and without even googling, there's Leesburg airport in Virginia

From this article I found the following:

The FAA has declared the Saab remote tower system at Virginia’s Leesburg Executive Airport (KJYO) “operationally viable,” authorizing ATC services to continue there using this system.
The system at Leesburg includes fixed high-definition cameras and controller displays, as well as maneuverable optical and infrared cameras, microphones, and signal light gun. Controllers at the remote tower have the same tools as at other ATC towers, but use live video displayed on monitors instead of direct vision to detect and direct in-view air traffic.
“This milestone FAA decision has positioned the Leesburg airport—the second-busiest general aviation airport in Virginia—one step closer to permanent ATC services, while avoiding the ever-increasing expense of constructing and maintaining a conventional, multi-story ATC tower,” Saab said.

I’m curious if anyone knows how the light gun is controlled and actuated.  Is it aimed visually by the operator or does it make use of a targeting system using dedicated cameras or radar?

Turns out answering whether this is controlled manually or automatically is doable (it's manual). Answering how it's controlled exactly is a lot harder unless you have the datasheet, which I don't. The system used (r-TWR, sometimes written without hyphen as rTWR) is part of Saab's Digital Tower portfolio so if you really want to know, try sending them an e-mail. Meanwhile I'll dump the information I gathered while trying to answer it with a conclusion on what it probably looks like.
To replace about a 100 aging control towers, the FAA is looking for a functional replacement that will:

Meet operational and cost requirements
Maximize energy efficiency
Be easy to modify according to height needs
Be rapidly constructed

Source: General Aviation News
That's a lot of buzzwords for indicating it's going to be a complete replacement of the tower and the same system should be able to work on multiple locations with only minor adjustments.
The proposed replacement active on KJYO is also active on KFNL.
Remote tower control room KJYO:

The rTWR system at Leesburg utilizes high definition video camera, a pan-til-zoom camera, a signal light gun, and microphones to provide data directly to controllers at a remote tower center located at the airport.

Source: GlobalAir
The article linked by Bageletas here (link) shows the cameras and sensors enable object tracking and anomaly warning. With the picture of the signal light gun, the following title is shown:

A signal light gun provides a backup if the system is faulty.

It's a backup system. None of the systems I've seen speak about any automation in a signal light gun. For example, the competition by Silent Sentinel has the Jaegar and Osiris, both mentioning they're capable of 'supporting additional specialist technologies including the signal light gun'. Which still doesn't tell us whether they can do it themselves or that they can support such a system when other parts are added.
The FAA doesn't speak about it either. The only functions of a Remote Tower Center (RTC) that mention a light gun are SLG and RLG.

SLG
Provides capability to communicate with aircraft,
vehicles, equipment, and personnel on the airfield and
surrounding airspace through visible light visual signals.

RLG
Remote control signal light gun capable of being directed in
azimuth and elevation to cover backup communication with
aircraft, vehicles, and personnel in areas of jurisdiction.

2.1.2 SIGNAL LIGHT GUN
The SLG must [R0184] provide the capability of transmitting signals in accordance with FAA Order 7110.65, 3-2-1, Light Signals.
The SLG function must [R0016] be capable of being verified for proper operation by the ATCS.
Note: Proper operation consists of the ability to direct and transmit the intended signal.
The SLG must [R0203] be capable of being directed at a target of interest.
The SLG function shall [R0204] respond within 250 milliseconds of operator input.
The SLG functionality shall [R0205] be capable of reaching a continuous rotational speed of at least 60 degrees per second.
The SLG functionality shall [R0206] be capable of reaching a continuous tilting speed of at least 60 degrees per second.
The SLG functionality shall [R0208] provide the capability of movement between two positions in the horizontal plane which are 60 degrees apart from a resting state to a resting state within 2 seconds, not including control latency.
The SLG functionality shall [R0255] provide the capability of movement between two tilt positions which are 60 degrees apart from a resting state to a resting state within 2 seconds, not including SLG functionality control latency.
The SLG must [R0015] be capable of being disabled in Maintenance mode.

2.1.7 CONTROL STATUS DISPLAY
Note: The user control includes interfacing with all the elements of the RT system necessary for the ATCS to fulfill their mission. Elements include RVP, SLG, Binocular Function, SVP, AAA, ancillary devices, audible and visual alerting, etc. Layout and design of control device(s), information display(s), and alerting methods need to provide a suitable human-machine interface design to minimize human error and maximize efficiency.

Source: FAA, remote tower systems requirements
So while the system itself is perfectly capable of tracking multiple aircraft, the FAA doesn't require the SLG to perform this function in an automated tracking capacity. The SLG must be capable of being directed and manually doing so is fine.
Considering the rest of the required functionality, a joystick might be part of the system but that would include a piece of hardware just for that task. From what I've read, the pictures that are shown and the experience Saab has with related systems (like I-ATS), I can say with relative confidence that the systems are primarily controlled by multi-touch screens or screen, mouse and keyboard.
These systems usually don't provide more functionality than required, even if they're capable. It's possible automated tracking will be added later as a feature, but that's a lot of work for a backup system. For now, it is manually controlled.
Note: I have no affiliation with either of the parties mentioned, although I have worked in the past for a company producing equipment for I-ATS.

The light gun is shown in this press release photo from Saab Sensis. It appears to be on a multi-axis pedestal with a camera, likely for tracking purposes.
Edit:Link to article with pictures

Thanks.  Any information on the user interface?  How does a controller point the gun?  Joystick? Touchscreen? If an a/c is squawking 7600 can the controller tell it to automatically lock on and follow it?  What if it’s just squawking 1200. Or has no xpndr at all?

@Jim unfortunately not. I could only find the picture!

@Bianfable it's been added thanks!

I’m really torn between the two answers here.  You were first and found a really good picture, and I thank you very much, but in the end I think I need to reward the apparent effort put in by @mast.

@Jim if I could give my extra votes to Mast I would! It's a well researched answer and certainly the better of the 2. Fun topic!


text:
TAS from POH or e6b
I always calculated my TAS at any cruise altitude by

Using my planned cruise (pressure) altitude, temperature
Plug desired CAS, PA, temperature into e6b and get TAS

But I've also seen people get TAS only from the POH for cruise. And many books say that e6b is only used for TOC and that for cruise you should use the POH.
The discrepancy I see is that the POH assumes a constant power setting. But I'm assuming a constant CAS. So, in that case it seems my way should be more accurate.
What's the proper procedure that a student pilot should follow?
p.s. I fly a pa-28-181.

You’re asking about flight planning, not in-flight use, correct?

there are many replies and comments on the identical Reddit thread

@StephenS yes, flight planning. Not in flight use

It doesn't matter, you'll get the same TAS either way as it's just a calculation.

Using the POH with a fixed power setting is more correct, and as a student, you should absolutely do it that way.
The POH is where you get your fuel burn per hour. That, combined with GS and ETE per leg (which you’ll get from TAS and winds aloft) will give you the fuel burn per leg, which is a critical part of your flight planning.

This doesn’t make sense.  TAS is simply the actual speed the AC is moving through the air. It is calculated from indicated airspeed by accounting for the density of air at altitude.  It has nothing to do with power settings.  The POH can only display expected TAS vs power settings for a nominal engine- which is often not the case in real life.

But OP says: Noting my cruise (pressure) altitude, temp.  This leads me to believe he’s in the airplane not planning.  Maybe I interpreted wrong?

Me either.  My ASI had a temperature knob and did the E6B calculation implicitly.  But in planning where would you even get CAS from??

@Jim I suspect OP is planning to fly a fixed IAS/CAS and adjust power as needed to achieve it. My CFI disabused me of that idea when I started XC flight planning.

Ok. May be. I agree- dumb idea.  It’s coming at it bassackwards.

Why is flying a fixed CAS a bad idea? this seems counterintuitive to me. If I fly a fixed power, then the plane has no idea of the environmental factors. So I'm basically letting the plane boss me around with what speed it wants to fly at. The timing aspect of XC only works if I'm trying to achieve my CAS. Am I having a big hole somewhere?

Because to fly a fixed CAS selected on a whim you will be constantly jockeying the throttle to keep it there. You will have no idea what your performance/endurance will be.  The proper way is to use the performance charts to trade speed for fuel/endurance and arrive at a desired TAS/power combination. Then you fly that power setting and hopefully get at least the airspeed you chose.  Maybe you’ll get more! Maybe you’ll get less and you’ll know you’ll need to take action to ensure you’ll reach your destination with the required fuel reserves.  Flying CAS you’ll have no idea.

@Jonathan In short: because that’s the only way you can predict your fuel burn and therefore know if you have enough fuel to reach your destination (plus reserves). That’s kinda important.


text:
What is significant in Diamond DA-42 over DA-40 apart from engine redundancy?

Aircraft/Characteristic
Diamond Star DA-40
Diamond Star DA-42

Span
11.94m
13.42m

Wing area
13.54 m²
16.29 m²

Max Occupants
4
4

$Va$
108 KIAS
126 KIAS

$Vno$
129 KIAS
155 KIAS

$Vne$
178 KIAS
194 KIAS

Max Take-off Power
180 HP
2×180 HP

Max Continuous Power
160 HP
2×160 HP

Max Fuel in one wing
25 US gal
26 US gal

MTOW
1200kgs
1785kgs

MLW
1150kgs
1700kgs

Max Altitude
16,400ft
18,000ft

My questions are:

Is the 50% increase in MTOW the only benifit of DA-42?

Despite having twice the power, there is not much difference in the cruising speed of the two aircraft. Why is that?

DA-42 has two engines - shouldn't that increase the fuel consumption and thus decrease the range?

Why was DA-42 introduced much later than DA-40, despite having such similar performance?

In regards to your questions:
1: like all twin engine airplanes, the benefit of a second engine is in a increased maximum takeoff weight, better, climbing ability, higher cruise speeds (combined with the retractable gear), and potentially offer greater redundancy.  The DA-42 is also turbo-diesel powered, giving superior high altitude performance and climbing abilities on hot days and/or high field elevations and operates on JET-A fuel as opposed to AvGas.  It’s also equipped with some additional systems, such as optional onboard WX radar.
2: The DA-42 is a solid 30 KTAS faster than the DA-40, and this really opens up above 10,000 ft, where the normally aspirated DA-40 lags.
3: Your onboard fuel stats are incorrect; while the capacities of the wing tanks are similar, the DA-42 also has two auxiliary tanks at 18 USG per side.  This fuel must be manually transferred by pump to the main tanks for use by the engines.  And the Austro engines in the DA-42 are very efficient burning about 8 gal/hr @ 95% power and 5-6 gal/hr @ 65% power.  An IO-360 will consume around 10-11 gph for a high speed cruise.  Given the 20-30 kt cruise speed difference for a given power setting plus the extra fuel, I’m not surprised at all that a DA-42 has longer legs than a DA-40.
4:  Different markets and Diamond was apparently not interested in manufacturing twins when the DA-40 was developed.

The difference in efficiency is in major part because they are diesels: diesels in general have about 30% better fuel efficiency (their main disadvantage for aviation is they are heavier for the same power).

There are DA-40's which have the exact same engine as DA-42's. DA-40's can be equipped with both the IO-360 and the AE300.

Yes, modern variants of the DA-40 now use the Astro turbo diesel engines. They (the DA-40NG) still don’t match the performance of the DA-42.


text:
What kind of maintenance is involved when an airframe has been overstressed (E.g. an F/A-18)?
In the movie Top Gun 2, the main character Over-Gs his aircraft (I think, an F/A-18 Hornet to around 10G).

From a maintenance perspective, what steps have to be additionally performed in order to get this aircraft back in the air?
What is the absolute limit at which the aircraft is permanently damaged?

A single overstress event is benign if you didn't permanently bend anything. That is, if the structure stayed within its elastic limits (like a spring), it's fine.
The inspection will be to look for permanent deformation from exceeding yield limits, and cracks or failures from exceeding ultimate limit loads (maybe where something failed, but there was a secondary load path in the design, so the plane didn't come apart).
In the end the absolute limit is the one that exceeds the yield stress limit for the first structural part to get there. Say, for a fighter, 8g yield (permanent bending) and 12g ultimate (wing spar or something breaks off).
There may be a published load limit, but there are fudge factors and a lot of variables, so you may have a 8g limit (maneuvering "red line"), but in a real event it may take 10 or 12 g to actually bend something permanently, and maybe 15g to get the wing to fold up.
When a commercial airliner gets overstressed, it gets a structural inspection, and if nothing is bent or broken, it's good to go.

Do you know how the procedure is for military aircrafts? Because I remember some crew chief saying that overstressing a military fighter jet requires some maintenance afterwards. However I think he did not mention if that is pure inspection or also the swapping of some components

Oh hard to say. I would guess "maintenance" just means inspection, but in the military they may use more conservative assumptions in view of the extreme operating environment, and say, replace things like bolts in critical areas as a matter of course.


text:
How do you maximize lift while keeping span as short as possible?
This weekend I saw the Fly Baby at the Smithsonian Air & Space Museum at the Washington Dulles Airport, and it was at some point the smallest airplane (since surpassed by the Bumble Bee II, if I understand correctly). To be able to carry a pilot and lift the plane off the ground in the first place, but still be the smallest airplane, you are mostly limited by wingspan, or more generally, the total width of the airplane.
For the purpose of this question I would like to assume a given airfoil and to exclude modifications to the airfoil itself, i.e. any mechanism that increases lift in pure 2D flow, e.g.  camber, slats, flaps, active blowing of the upper surface etc. I would like to limit the scope to the "3D planform" of the wing(s) - e.g. aspect ratio, sweep, depth, winglets/end plates/..., box wings, number of wings etc. The airplane needs to have a fuselage that holds the pilot and an engine. Otherwise the configuration can be whatever it needs to be. If the configuration for maximizing lift depends on the choice of airfoil, then just assume a suitable airfoil.
Both record-holding planes are biplanes, with the Bumble Bee having a relatively large horizontal stabilizer. It also has endplates on the wingtips, reducing lift loss due to the tip vortex.
How can one maximize the lift for a given width?
(I could list all of the ways that come to mind and ask whether and how much they help, but then I'd have "more than one question" and I'm not sure that would be suitable for this format)
Edit: Further clarification: I am asking about maximizing the coefficient of lift of the entire airplane, not about lift itself (which could be maximized by flying faster, to a certain extent). Also, I would like the answer to be valid for low flying speeds (incompressible flow).

You're right, I meant the plane needs to only carry a single person. From my understanding, the airfoil is the 2D cross-section of the wing, and the wing is 3D, being a simple extrusion of the airfoil in a straight line, or tapered, or swept ... I tried to add some precision to the question. I wanted to exclude the airfoil and all the tricks to maximize lift in 2D (some I've listed in the question) because the scope would be too large.

I clarified further that I am indeed asking about coefficient of lift of the entire plane (yes, fuselage shape has an effect, but speed and weight don't). I think it is very well answerable, since I am pretty sure I am not the first one to think about this, but I personally lack the understanding of intricate 3D flow around multiple wings, that's why I am asking. E.g. could the lift be improved on the mentioned designs by turning the biplane wing into a box wing (everything else being equal)? Is it maximum for 2 wings, or can one add more?

The basic design limitations are rather confined, but one must consider the airfoil as a variable in developing that design.  Major controlling factors are wing loading and power. One needs sufficient airspeed to get the lift required for flight.

Of course, any wing arrangement really (triplanes, box-wings, tandems ...).

By "narrow wing" do you mean a small wingspan?  That is not how most readers will intuitively understand your question.  I'd suggest an edit that employs terms like "span" and "chord" rather than terms like "narrow" and "width".

Unfortunately, lifting fuselages are not as good as wings for slow flight, although the albatross does a wonderful job making it as good as it can.  High aspect is the way to go, avoiding wing tip (plates) and fuselage (fairings) interference as much as possible.

@quietflyer The question title was edited by somebody else in the meantime ... I'll change it back to something more accurate.

Ever think of trying this?

Some of your parameters are extraneous distractions. Do you want to maximize lift coefficient for a given wingspan/width, or do you want to minimize wingspan for a given useful load(pilot & fuel) and airspeed? These goals are in direct conflict as you cant maximize lift while keeping lift fixed nor minimize wingspan while keeping wingspan fixed.

A gyrocopter has a extremely high lift coefficient and can be further improved by stacking rotors and adding blades per rotor, unlike a conventional airplane where you run into diminishing returns quickly when the aspect ratio is too low.

The Chance Vought V-173 "flying pancake" was designed to provide low speed flight with very low aspect ratio wings. In fact, the entire body is a wing and the twin propellers are arranged to blow their slip stream over that body. It could very nearly hover, so the lift coefficient is extremely high.

With modern flight control computers the vestigial horizontal tail could be incorporated into the rear fuselage as is done with flying wings. You can see that this has already been done with the center part of the tail. If you were concerned about the width of the props, they could be moved inboard and wing twist altered.

The flaps at the "center part of the tail" on V-173 are not control surfaces. They serve to reduce the massive ground effect this airplane had on landing. They only moved upwards and were added later when the problem with landing was discovered. The stubby "wings" on either side are just elevons and are entirely in the prop slipstream to allow control at low speed. The props, by the way, rotate outwards to counteract the tip vortex, which significantly increases the effective wingspan. (Or should we call it "bodyspan" here?)

@Zeus Good info on the tail.

The only significant option you have within the parameters given is to increase the chord. And this has no maximum unless the plane also has a maximum length. but then you increase effective wing area by vertically stacking more wings, again like cord theoretically infinite unless you have a height restriction.
Wingtip devices are effective but rather binary in nature, either you use them or don't, their isn't any real scaling involved other than matching the general size of the wing. They also add weight, which is why they are popular for long haul where fuel is a large fraction of payload but not short haul where the added weight causes more fuel burn than the aerodynamic savings. Many many variables, maybe too many to fully account for with current engineering tools and knowledge, at least for a question like what is "best".
By the way the bumble bee was a terribly unstable short range racing plane. The Bee Gee was the short wing speed record and racing airplane. It was designed to get lift from speed and minimize high speed drag without regard to low speed effectiveness.The Bee Gee was the short wing speed record and racing airplane.

@quietflyer Don't spam the comments.

@quietflyer ah yes I was thinking of the GeeBee not BumbleBee I will edit that.

... camber, slats, flaps, blowing of the surfaces

Unfortunately, they are some of the best ways of increasing Coefficient of Lift, far better than trying multiple wings, as seen with the Fiesler Fi 156 Storch.
Deep camber, undercamber, increasing chord (and, proportionally, thickness) are helpful in particular, as are endplates.  Another wing or two can be added.
Weight should be reduced as much as possible with safe structural strength requirements in mind.
But now you have a very draggy, slow aircraft with limited range,
unless you can retract these devices and speed up a little.

Lift is proportional to V$^2$

If you have even more power, and the option to go supersonic, a short single wing like this
or a lifting body with no wing at all like this one would suffice.
It really depends on your fuel budget and available thrust.  Cost conscious subsonic airliners use retractable lifting devices, and even slower speeds are required only because of airspeed limits, runway length, and the quality of the landing gear (especially tires).

Keep in mind some of these "record setting" aircraft may not be very safe to fly

Lift is also proportional to S.

"... not very safe"  Indeed - don't think about turning in that thing!  Ok, maybe 5 degree AOB...

The question explicitly says not to alter the basic airfoil. Increased cord implies proportional thickness if the airfoil designation is unchanged.

@MaxPower actually, the question specifically says fly slowly.  If you want to argue how it's been done for 100 years, be my guest.  BTW, the answer does include increasing chord, did you see it?

My reading comprehension is just fine. "I would like to assume a given airfoil and to exclude modifications to the airfoil itself, i.e. any mechanism that increases lift in pure 2D flow, e.g. camber, slats, flaps, active blowing of the upper surface etc. "

@MaxPower we read on then about increasing Coefficient of lift, and my second reference to the DAE 21 (and bird wings).  Undercamber is key to increasing Coefficient of Lift.  This is really "mission impossible" as seen in the high stall speeds of current designs. (Notice the "pancake" is blown). Let's move on.

Coefficients are relative, while the common convention is to use horizontal wing area as the reference it is not the only reference that can be plugged into the equation. The only catch is that like must be compared with like, so a frontal reference area coefficient or width based coefficient[this case] could not be numerically compared to a plan-form area coefficient.

@MaxPower the Lift Equation takes care of all that.  Unfortunately for the OP, body lift does not work very well at low speeds.

Do you mean low speed as compared to compressible supersonic flow, or just a change in speed within the incompressible speed regime?

@MaxPower Within the low Mach "incompressible" range (circa 1918) Gottingen made some really good low speed wings.  V$^2$ has the most powerful effect on lift.  For very slow flight, you are right if not changing the airfoil, span should increase with chord, or stack multiwings.  Increasing lift coefficient (with more camber) is also useful.

Just increasing chord (and reducing weight) would give one something akin to a paraglider with horrible handling in the wind and not as great lifting efficiency.  Large square wings (eagles) are useful in strong thermals (have a look at a clipper square rigger), but lack lifting efficiency (have a look at a schooner or an albatross).  The "pancake" works at low speeds because it's blown, and at high speeds because of low drag.


text:
Why is it assumed on sectionals that the area outside of a 700 AGL Class E (Echo) transition area is Class E starting at 1,200 AGL?
In this Bold Method article (http://www.boldmethod.com/learn-to-fly/airspace/class-g-airspace/) it is stated that anything beyond the hard lines of this examples 1,200 ft AGL Class E (blue) transition area is Class G (Golf).
So far so good.

However, further down in the article, it is stated that beyond the hard lines of the magenta 700 ft AGL Class E transition area that the airspace is Class G until 1,200 ft AGL at which point it turns into Class E again (think the blue Class E area that exists above this entire area).

Why is it assumed that outside the 700 ft AGL Class E transition area there lies 1,200 ft AGL Class E? It surely isn't represented in the screenshot. Couldn't it just as well be Class G until 14,500 ft AGL?

Take a look at the legend on the side of a VFR chart. (You can get them for free at https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/vfr/ )
Class E exists at 1200' AGL unless otherwise designated as shown above.

I don't know why I didn't bother to re-read the legend, thank you for the answer. This legend however indicates that the magenta Class E doesn't necessarily have to be against a 1,200 ft. AGL Class E. It is possible to be against Class G. Do you know of any examples where this situation can be found?

Even though I’ve read the legend hundreds of times, I missed it as well until you asked the question.

There are actually only a handful of places in the us where the 14,500 Class G exists. Check out http://aviation.stackexchange.com/q/29523/8730

If you are bored sometime, try to figure out all of the different floors and ceilings of Class G around Death Valley and the Saline MOA.

So does anyone know any examples where the 700' Class E floor actually does laterally abut against class G airspace, as depicted as a possibility on the chart legend in this answer?


text:
Why do Western aircraft manufacturers use FPS system while Russian aircraft manufacturers use MKS system for flight instruments?
Why is there a variation in aircraft flight instruments of aircraft from Western & Russian origin?

Foot–pound–second system (FPS)
Meter-kilogram-second (MKS)

Interesting question. But according to this https://aviation.stackexchange.com/questions/2566/what-is-the-measurement-system-used-in-the-aviation-industry you are asking for a reason for a non-fact so it's impossible to answer. China isn't entirely metric in reality because a few "native" units are still in use, like their version of inch (33mm), foot (330mm), mile (500m), etc. So I would say the resistance of introducing "yet another standard" is understandable when metric is "yet another" already itself.

Units of mass isn't uniform. Western aircraft can be switched over to kg by operator's preference, usually just a setting for the software. (Such a changeover caused the Gimli Glider accident) Further, many western aircraft have a metric display button for flying in metric airspace.

@mins It wasn't. The fueler always expected liters. The crew used the conversion factor for liters to pounds then pounds to liters, when they were computing liters to kg, then kg to liters. This was because the 767 was configured for kg instead of their earlier pounds.

According to ICAO, the use of non-SI units is a temporary measure, as most countries in the world use SI units in other domains, including research and engineering (US being a notable exception). However Western aviation organizations are very reluctant to change feet into meters. Related: Standard Application of Units of Measure in Civil Aviation.

Why is there a variation in aircraft flight instruments of aircraft from Western & Russian origin?

As so often in aviation it's a result of WWII. In continental Europe, and this includes Russia, MKS was until the end of the war standard, while the US and GB used FPS. After the war, Germany as major standard proponent in aviation 'vanished', flying in western Europe was basically defined by US measures - including measurements, while on the other side of the iron curtain MKS was continued. This meant not just the USSR, but all eastern European states. China in turn acquired most of its flight technology from the SU, including regulations and measurements.

Why do Western aircraft manufacturers [...] while Russian aircraft manufacturers [...]?

It's also less an issue of manufacturers, as of regulations within these states. Boeing is happy to deliver 787s to Russia with all metric instruments - the same way Suchoi would frolicking to equip Superjet 100s with FPS to be sold in the US :))

The short version is that "Western" countries (nearly all countries, in fact) use knots and such because that's what we started with and, once that became entrenched, the cost of retraining every pilot and reequipping every plane--and the inevitable confusion and crashes during that transition period--greatly exceeds the benefits.
The USSR, PRC and a few others were able to use metric units because they didn't need to care about compatibility with the rest of the world--or perhaps saw the lack of compatibility as a good thing, helping to keep them isolated.


text:
How does the ski shape of an aircraft carrier deck help for take off?
Why is a ski-shaped deck used on an aircraft carrier for take off?
The aircraft needs a particular lift for a particular weight, how does ski assist in take off?

Are you talking about the sled where the gear is attached to pull the aircraft down the deck? Do you have a picture of what you are talking about?

Or  a "ski-jump" flight deck?

The Ski jump was originally used by the UK Royal Navy to assist Harriers in getting airborne.
The Harrier cannot take-off vertically when fully loaded.  In all models, the thrust is lower than the maximum weight.  Therefore, they need to do a "short take-off" where the thrust nozzles are angled rearwards to provide thrust, then partially angled downwards as speed is gained to produce enough lift from the wings, and thrust angled downwards, to climb away.  Watch the nozzles closely at about 17 and 36 seconds in this video.  Try not to watch the poor chaps forehead too closely at 20 seconds.  Also watch this video.  At about 16 seconds, you can see the pilots left hand pull back on the nozzle angle lever as he passes the end of the deck.
Now imagine a flat deck on an aircraft carrier.  Operations must be able to carry on in rough seas.  You accelerate down the deck and fly off the end, just as the deck dips downwards as the carrier rides a large wave.  You are pointed straight at the sea.  In order to avoid flying into the sea, you need to climb, which means pulling G and a lot of power at low speed which the Harrier just didn't have.
Now consider the ski jump.  There are two effects.

The jump is angled so that even in the worst seas in which operations will continue, the bow pitching down will not point an aircaft leaving the end of the jump towards the sea.  The aircraft will always be pitched upwards.
Imagine driving a fast car up the jump and off the end.  It will be thrown up and forward in a parabola.  Even a car, which cannot fly, will be pointing up for a few seconds, then level for few seconds before falling into the sea.  But instead of a car, you are driving a jet which can fly and has thrust.

The aircraft will angle the nozzles rearwards for maximum acceleration until it leaves the jump. The wings are now generating significant lift, let's say 50% of that required to climb away.  As you leave the end of the jump, you angle the nozzles downwards so that you have the momentum of the aircraft and some rearward thrust maintaining lift on the wings whilst adding lift from the thrust vector having a downward component.
Those seconds of pointing up, then level, enable the aircraft to continue to accelerate until all of the lift required can be gained from the wing when the nozzles can now be angled rearward again to continue the acceleration. Take-off speed is therefore reduced and take-off distance is about halved meaning smaller, cheaper carriers.
That's how Harriers do it.  I imagine it's the same story for any other VSTOL aircraft.

Heh, "We couldn't get the whole aircraft carrier in" --The poor chap with the unfortunate forehead.

https://youtu.be/rc5G04nJecI

Thanks for the warning about the 20 sec point.  I would have missed it otherwise.  ;)

@PJNoes A real Waynes World moment :)


text:
What is the benefit of upgrading Flight Management System to version UNS-1Ew?
I am working in a private airlines. We have some Dash-8 Q400 aircraft in our fleet. Recently a SB has been issued telling us to upgrade the Flight Management System from  UNS-1E to UNS-1Ew.
Can anyone explain what are the advantages for upgrading the Flight Management System from UNS-1E to UNS-1Ew?

Here is my understanding of the update. As others I believe your primary source should be your OEM.
Main purpose: Ability to use SBAS procedures and navigation
The purpose of moving from UNS-1E to UNS-1Ew is getting the SBAS capability. From the UNS-1Ew manual:

The new “W” series of Universal Avionics Flight Management systems
  incorporate the Global Navigation Satellite System (GNSS) Space Based
  Augmentation System (SBAS) known in North America as the Wide Area
  Augmentation System (WAAS). Other SBAS systems in the world will also
  be incorporated.

SBAS details
SBAS means using WAAS, EGNOS and other GNSS augmentation systems. SBAS in short provides for correction of GNSS radio signal propagation errors in a limited area. This increases pseudo-ranging accuracy and positioning precision.
SBAS (space-based) is opposed to GBAS (ground-based) where correction broadcasting stations are on the ground, like the DGPS, a surveying GBAS with a positioning precision up to 10 cm.
EGNOS measuring network (SBAS for Europe area):

Source: Wikipedia

Additional benefits of the update
From UASC documentation:

What else you get with an SBAS-FMS upgrade:
•  Performance-Based Navigation (PBN) including Precision-Area
  Navigation (P-RNAV) compliance and Required Navigation
  Performance/Area Navigation (RNP/RNAV) up to 0.3 NM approach accuracy
• WAAS LPV / EGNOS APV, LNAV approaches
• Mode S Enhanced Surveillance support
•  Accurate SBAS-GPS information provided to the onboard Terrain
  Awareness and Warning System/Enhanced Ground Proximity Warning System
  (TAWS/EGPWS) and Traffic Collision Avoidance System (TCAS)
•  Large database capacity for worldwide navigation databases

You can read "The Benefits of SBAS" on UASC site.
And if you need more information the UNS-1Ew manual is also available.

Don't forget that ADS-B requires a WAAS capable receiver.


text:
Which frame of reference is used to calculate ground velocity?
During flight, in which frame the ground velocity components are calculated? in the body frame or in the earth frame?

If you want ground velocity why would you use anything other than the earth's frame of reference? Nothing else would actually be the ground velocity.

@mins that's true, question needs more information I think.

The answer is already in the question. Ground speed refers to the ground. That directly implies earth as reference frame.
The speed of an aircraft relative to itself is apparently 0.

@mins: … and the readings could all be caused by drift while the aircraft is still at rest on the ground. Inertial units are fine for accelerations, but poor for speeds - that is why you still need air data sensors.

The answer to this question lies in what you are trying to evaluate, which is unclear.
Ground velocity could be interpreted to literally "the movement of the ground with respect to the body". In this case the frame origin would be the aircraft (body). Or ground velocity could be interpreted as the velocity of the aircraft with respect to the ground, (frame origin ground). The question is moot for just ground/aircraft or aircraft/ground because one should be the negative/opposite of the other. However, if one is trying to calculate the velocity of one aircraft to the velocity of another aircraft the choice of frame will simplify/reduce the calculations needed to find that value.


text:
Do air-driven gyroscopic instruments suffer from icing or any blockage of filter?
Do gyro instruments suffer from icing in an air-driven gyro system? Do they have any particular way to protect them against blockages of filter or any type of other blockage? (Alternate source?)
I am more concerned on light aircraft C152, C172, PA28, etc.

From all that I have seen on that type of aircraft, there is merely a filter.  If one was operating in a dusty environment (eg the bush) then I would add those to a 100 hour check.  But honestly, I have never seen one clogged to the point it would not work.
They are not suspectable to icing as there is a low pressure drop across them, and they get their air from inside the cabin, where there is not a cold mist. It's usually rather dry and at low temperatures, it is probably heated.
The alternate air is for the static port, which is exterior, and will ice up, although it is a rather infrequent occurrence. The altimeter, airspeed and VSI are not gyro instruments, and are impacted by the static port. Keep in mind that if your altimeter is not reading correctly because of static port ice, then most likely your encoding altimeter is similarly off, and your mode C (or other) readout at ATC will be off. In my experience, the Cessna models you listed tend to ice less than the PA28 models, but again, it is rare, even for weather flyers. And if it is happening to you, you need to reexamine your weather choices.
While we are talking blockages, the pitot tube is the most frequent, and there have been times that I have had to remove a bug from the tube on the Cessnas. Let a mechanic do it the first time, so that you get some of the tricks. I usually use a straightened paper clip or a piece of safety wire, with a sharp hook, about 0.3mm bent in it. That will help you scoop out the bug.  Again, this doesn't happen often, as usually we have covers on pitot tubes, but I have had it happen in remote areas (like Central American hilltop unimproved airports) so if you are flying to those places you need to make friends with your mechanic so that you can manage the lots of different things that come up.
In summary, the vacuum gyros have a filter, and they don't tend to clog often. Some of them are rather coarse, but modern ones have 10 micron filters or better. If you are in an extremely dusty area, they should be periodically inspected. For most people, they will never have a problem with them.  (If you have that much dust in the cockpit, then you will have other problems, including avionics switches, dirt creeping into displays, etc.)

You said that the air-driven gyroscopic instruments take the air from the cockpit, can I see the filter from the cockpit? Is it possible to check visually if it is clogged? Thank's

For the aircraft mentioned, you will need access to the back of the instrument panel.  This is something best done by an A&P or avionics tech.  For many but not all, the filter surface is visible or partially visible, but it might be necessary to extract the instrument from the panel to get a good view (normally 4 screws, vacuum line and lamp power if equipped).


text:
What's the difference between FAA Part 61 and Part 141 training?
I've got schools with both part approvals in my area. I'm just interested in recreational flying, I'm not sure which part is more suited to my needs.
What are the differences I should consider before choosing one or the other?

I am not sure that the question is really opinion based. I am not from FAA land, but to me it seems that Part 61 and Part 141 refer to FAR 61 and FAR 141 which are textually very different. I assume that someone knows or will go through the trouble of finding out what those differences are and what the implications are for training.

I think you need to cite the case that may drive your decision one way or the other.  Context is important here.  FOr practice, let's close this, and then if someone edits it then they can vote to re-open it.

@DeltaLima: yes, generally Part xx refers to the FARs, where not otherwise specified. EASA regulations come under CS-XX numbers, and other authorities have different things.

@TheWhiteDiamond I did this originally and I think the question is too specific to me. The existing edit made it more general.

There's no singular right answer, it's up to the individual and how he or she learns best. The biggest difference between the two you'll find is that part 141 schools are always very structured in their training regiment. That is not to say part 61 isn't (nor does it imply that it's better for everyone), it's just that part 61 does things according to what they wish with less FAA oversight.
You might know that under part 141, the earliest you can get your ticket is 35 hours, while part 61 requires a minimum of 40 hours. Don't let that red herring influence you; almost everyone takes more than 40 hours regardless of the school type.

I did my training at a Part 61 school, but we followed Jeppesen's Part 141 syllabus. So the differences can be minimal if choose that route.
Not relevant to Private Pilot training, but an important difference between Part 61 and Part 141, when it comes to Instrument training, is that Part 61 requires 50 hours of PIC cross-country, whereas Part 141 does not.
When I wanted to start my instrument rating, I only had 25 hours PIC cross-country, so Part 141 sounded appealing to me. Having recently moved to New York City and not knowing anyone in aviation here, I called the owner of a Part 141 school, and immediately disliked him. He was arrogant and egotistical and didn't care about anything I had to say. He just wanted to brag about his airline experience and how organized his school is... then didn't even call me back at the time he said he would. So I called up another flight school and immediately liked them and went flying with them the same week. Unfortunately they're only a Part 61 school, but the fact that I like them is a big win.
TL;DR
The point is, the biggest difference between any two schools is not actually 61 vs. 141, it's the people who run it, and whether or not you mesh with them. Unless you have commercial ambitions (where Part 141 might help get you where you're going faster), base your decision on the people, not the part.


text:
Are jet aircraft still at risk of hijacking by people wielding melee weapons?
Are jet aircraft still at risk of hijacking by people wielding melee weapons (as opposed to explosives)?
I thought that aircraft were designed post-9/11 such that passengers can't enter the cockpit, but Wikipedia's list of hijackings mentions incidents this decade which involved melee weapons:

China June 29, 2012: an attempt was made to hijack Tianjin Airlines
  Flight GS7554 from Hotan to Ürümqi. Six people tried to hijack the
  aircraft 10 minutes after take-off. There were 6 police officers on
  board. Four were in plain clothes, taking the plane for a business
  trip. The hijackers used aluminium canes with sharpened tips to attack
  the members of the crew. The police officers and civilians on board
  subdued the hijackers, all of whom were of Uyghur ethnicity. The plot
  was foiled and the plane returned to Hotan in 22 minutes after
  takeoff.

Welcome! Could you provide the reference of a case where a passenger entered the cockpit since 2010? The list you currently reference seems to include only cases of alleged bomb on board, and copilot involvement. I understand attack the members of the crew as a violence against the flight attendants, in the cabin. The latter type of threats cannot be prevented, as so many objects can be used against a person in the cabin (a belt can be used to strangle someone)

United Airlines Flight 93 history shows that melee weapons are not very efficient: the passengers that are likely to outnumber hijackers at least ten to one can win if they are willing to fight.
The question remains, how likely is that passengers will go into risks to show the resistance. If it is just about changing the course to land in the different airport, they may choose to be quiet. If they have nothing to lose, I think the hijackers have no chances.

You might want to rethink citing a case in which everybody died as an example of ineffectual hijacking.

It is still a hopeless failure for plan the hijackers have had, very discouraging from trying again.

There are two answers.
Practically speaking: no.
Technically speaking: yes, but only if they meet little to no resistance from the passengers or crew.
Passengers in the US have proven on several occasions that they will fight (and even kill) troublemakers on airliners.  Many flight crews are armed, too.  I think passengers understand that "modern" hijackers probably intend to destroy the airplane in some highly visible, highly destructive fashion.  Given the option of simply riding the plane into the ground or getting wounded fighting against a hijacker, most people will arrive at the conclusion that they are more likely to survive by fighting back (even if hijackers claim to have a bomb).
Personally, if presented with the option of being slashed with a box cutter or killed in a plane crash, I'll take my chances against the box cutter...and I think two or three other large guys would join me.

"Many flight crews are armed": You're likely talking about the US, because in nearly all other countries carrying a weapon, unless you are in the police, is illegal.

Yes, in the US.  Part of "Security Theater" brought to you by the DHS.

Israeli airline El Al also has armed staff.


text:
What are these aircraft at AMARG? Why are they dismantled this way?
At the AMARG boneyard (Tucson desert, Arizona), there are tons of aircraft, but a limited number of models are dismantled according a special way: wings or tail or both separated from the fuselage:

Image from Google Maps

Source, reframed
I doubt all tails will suddenly be used as spare parts...
What are those military aircraft? why are they systematically dismantled this way?
(Not sure the question is on topic.)

Some B-52s and other aircraft were put out of commission as part of the START treaties.  They were dismantled in such a way that the Russians could verify this with satellite reconnaissance, just as in the photo above.

So apparently the B-52s were sold for scrap, but for some reason are still at AMARG after the 3-month period of satellite observation. Does that means that other aircraft are not in the scope of the START treaties?

@mins I've no idea. The Google image could be old - perhaps more recent imagery has been classified? The B52s were classed as "nuclear delivery systems" if the tail was still on - even though they were in the boneyard. Whether they are still there or not, who knows?


text:
Why is "NoPT" indicated on this KYKM approach?
For LOC-DME approach (back course) at Yakima Air Terminal (KYKM), NoPT was mentioned at different locations on this 2008 plate:

Click for full plate. Source.
However there is no procedure turn at all. Why is NoPT mentioned?

FAA_H_8083-15B Instrument Flying Handbook 2012
Procedure turn. A maneuver prescribed when it is necessary to reverse direction to establish an aircraft on the intermediate approach segment or  final approach course.
This particular approach doesn’t have a course reversal—the DME arc takes care of the course change from the YABLU IAF and the DATVE IAF. (Cut off on your map.) BABRE is an intermediate fix, and again needs no reversal.
So as you mentioned, there is no reason to state NoPT.
The version of the chart you used in your post is out of date. The current chart doesn’t mention NoPT, probably because there is no reason to. I’m guessing that mentioning it on your version is a mistake that they have since corrected or they are conforming to newer standards for chart making.

As you can see from the sides of the chart, your version of the chart is from 2008. The current version doesn’t show NoPT at any of the four IAFs. I also randomly looked at a dozen or so procedures in ForeFlight and the only time I can find NoPT is if there is a charted procedure turn. I have a set of Jepp charts from 2011 and same thing is done on theirs. I'm guessing that at one point there was a procedure turn for approaches coming from directly over the VOR and they forgot to remove the notation.

Did the altitude restriction change when the "noPT" was removed?

@radarbob Yes. The current altitude restrictions are 5800 from YABLU to BABRE (the bottom arc) and 7000 from BTVE to CADED dropping to 5800 to BABRE (the top arc). The arc is now 17 DME. Lots more waypoints and two more IAFs as well.


text:
Why is there an ETOPS marking on the nosewheel door?
What is the reason for painting ETOPS on the door of the nose gear?

"ETOPS" marking on a B737-800 (source)
Markings on the belly are supposed to be useful for ground handlers, what is it supposed to do here?

You're correct that it is for ground handlers; more importantly, it is for mechanics. It is important to identify the aircraft as ETOPS as the servicing and checking requirements are different for ETOPS and non-ETOPS aircraft. For ETOPS aircraft, two critical systems (like engines) should have differnt maintenance personnel to avoid them making the same mistakes in both of them.
From 14 CFR § 121.374 Continuous airworthiness maintenance program (CAMP) for two-engine ETOPS:

(c) Limitations on dual maintenance.
(1) Except as specified in paragraph (c)(2), the certificate holder may not perform scheduled or unscheduled dual maintenance during the same maintenance visit on the same or a substantially similar ETOPS Significant System listed in the ETOPS maintenance document, if the improper maintenance could result in the failure of an ETOPS Significant System.
(2) In the event dual maintenance as defined in paragraph (c)(1) of this section cannot be avoided, the certificate holder may perform maintenance provided:
(i) The maintenance action on each affected ETOPS Significant System is performed by a different technician, or
(ii) The maintenance action on each affected ETOPS Significant System is performed by the same technician under the direct supervision of a second qualified individual; and
(iii) For either paragraph (c)(2)(i) or (ii) of this section, a qualified individual conducts a ground verification test and any in-flight verification test required under the program developed pursuant to paragraph (d) of this section.

In the same vein, from Boeing:

Strategies for Avoiding Multi-Engine Maintenance Errors
After investigating several multi-engine maintenance events, Boeing identified a key strategy for avoiding multi-engine maintenance error: If possible, operators and repair stations should avoid performing maintenance on multiple engines using the same personnel during a single maintenance visit. Following this strategy should also minimize the potential that improper maintenance will occur on redundant or backup critical systems, such as flight controls, electrical generation and distribution, and hydraulics.

If the NLG doors have ETOPS written on them it would be easier for the technicians to identfy the aircraft and perform checks/maintenance as required, using two different operators, if required.

Perhaps more importantly, it's for pilots!  Within a single operators fleet, it is possible for one aircraft of a particular type to be ETOPS rated and another not.  This has resulted in crews flying the wrong aircraft.

@Simon Yeah, that's especially true for an airline like Southwest where they have several hundred 737s (they're the world's largest 737 operator,) but with only a small percentage of those flying over-water routes. Especially when you have a last-minute equipment change, it's good for the pilot to be able to quickly confirm in the walk-around that the plane he's about to fly is indeed ETOPS certified when it needs to be.

@reirab: Hum, that may help a bit but it definitely not enough and could be dangerous if ETOPS 180 is required and this aircraft is only ETOPS 90. So an additional information is required, and when found makes the gear door marking redundant.

@mins As far as I know, that's not currently a problem with Southwest, since they only have one type of ETOPS-certified aircraft. :)

@mins Actually, I'm not even sure they've started ETOPS routes, yet. Apparently they're planning to start flying to Hawaii, though.


text:
Which air stream pressure / speed is measured by the pitot?
The pitot tube is used to measure the air pressure later converted into air speed. However air pressure varies according to several elements, including the location related to the wing:

(Source: av8n.com)
On one hand the probe, depending on its location, could measure the pressure in the free stream, in the high velocity stream, or in the low velocity stream.
On the other hand, pitots are found at various locations, e.g:

On the fuselage, far from the wing, B-737 (source)

On the vertical stabilizer, kit Nemesis NXT (source)

Under the wing, Cessna 172 (source)
Furthermore when the probe is fixed to the fuselage or to the stab, depending on the angle of attack, it can be rotated into the slowed down or the accelerated portion of the stream.
Can you shed some light on what is usually measured by the pitot? Does the pitot indicate different pressures if placed in the different stream areas (free, accelerated, decelerated)? If so:

What is usually measured by the probe?
What is usually displayed on the speed indicator?

Edit: While I needed to select a single answer, several other answers contain additional interesting elements and deserve votes as well.

You're correct that there are a number of parameters that influence the measurement of air data in general. For example, the total pressure measurement (as done using the Pitot tube) is influenced by,

Angle of attack
Reynolds number
Mach number
Velocity gradients
Proximity to surfaces (wings, fuselage etc.)
Flow steadiness
Probe geometry
Compressibility and shock
Shape of the measuring head etc.

In case of total pressure, as long as the (pitot) tube is outside the boundary layer and the flow angle is less (<10% usually), the error is negligible. The following image shows the error due to incidence angle at different speeds for different head designs. Here, $H_{0}$ is the Free stream total head es measured in the tunnel intake and $H_{1}$ is the head measured by the instrument.

Image from Tests on the Effect of Incidence on some Pressure Heads at high Subsonic Speeds by E W. E. Rogers, D.I.C., & SC and C. J. Berry,
From the same paper:

Tunnel measurements have shown that up to at least M = 0.75 the loss in total head on a Venturi-shrouded pitot was less than 0.5% for incidences of up to about 40$^{\circ}$. This compares with a limit of 9$^{\circ}$ at M = 0.7 to 0.85 for 0.5% loss on the pitot section of a standard Mk.VIIIA instrument and 17$^{\circ}$ at M = 0.7 to 0.9 on the small pitot heads in general use ...

Static pressure measurement errors are similar; however, there are some points where the errors in static pressure measurement in the fuselage of the aircraft are minimal and the static ports can be mounted at these points (in addition to the static port in pitot-static tube).

Image from Airdata Measurement and Calibration by Edward A. Haering, Jr.
NASA Dryden Flight Research Center
It would be better if the static ports are mounted at these points in order to reduce the error.
From the above data, it can be seen that for GA and commercial aircraft, the position of the pitot-static tube can be located with reasonable accuracy at a number of points as long as it is in the undisturbed flow.
Another point is that the pitot-static tube measures pressure and the Air Data Computer (usually) converts it into the required parameter (for eg. speed). So,if the errors are known (during flight testing, for example), the instruments could be calibrated as per requirements. In general, typical methods used for calibration are,

Tower Flyby
Trailing Static or Trailing Cone
Pacer Aircraft
Radar Tracking
Dynamic Maneuvers

among others. Other electronic methods are also used for calibration purposes.
In order to achieve the very high accuracy required during flight testing and to serve as a reference, air-data booms are sometimes used in experimental and test aircraft, as can be seen in the F-35 below, whose data can be used for calibration.

"Cockpit and Air Data Boom F-35C" by File:CF-1 flight test.jpg: Andy Wolfederivative work: Berg2 (talk) - File:CF-1 flight test.jpg (cropped). Licensed under Public Domain via Wikimedia Commons.
In some extreme cases, the nose mounted airdata systems which are typically used (to minimize influence of aircraft on measurements) can be unsuitable due to specific reasons. A good example is the NASA F-18 High Alpha Research Vehicle (HARV) program, where,

... a noseboom was deemed unacceptable for this program. At high angles of attack, the noseboom has a significant effect on the forebody aerodynamics and thus on the stability and control of the aircraft. As a result, wingtip mounted sensors and a flush nose-cone mounted sensor were used.

Do probes on the three examples in my question measure the actual free air stream speed (pressure)?

@mins, it does not measure speed at all. It is not intended to! The "indicated speed" is really dynamic pressure and this is intentional, because lift depends on dynamic pressure, not speed. It is just expressed as speed it would correspond to at specific conditions (101.325 kPa and 15°C).

@mins, AFAIK the B737 has static port and appears to be placed in the point 2 on the pressure distribution diagram to minimize error. The C172 one does not seem to have static port and as explained above, the total pressure is the same anywhere outside the boundary layer; the error depends on how well the static port is placed. The middle one is probably similar case with separate static port.

The first thing to have in mind is that a pitot tube is NOT measuring speed: the pitot tube measures pressure and later on the airplane (flight management system in a modern airplane) calculates the speed based on pressure.
More specifically the pitot tube calculates the stagnation pressure which is the sum of static pressure (what you show in your picture) and the dynamic pressure (pressure obtained by stopping the air).
The total pressure remains constant in the external free flow in normal airplane operations BUT will not remain constant in the boundary layer, which is a small region close to the wall. The boundary layer grows with the distance downwash along the airplane.
What I explained here justifies the following design solutions:

Pitot tubes are usually installed with an small distance to the walls "like floating" in order to be outside the boundary layer and free of loses on the stagnation pressure.
Pitot tubes are never installed at the tail of the airplane, in order to avoid high thickness of boundary layer (could reach 1 meter).

Essentially C-172 is having the probe located in the very beginning of the wing, not contaminated by any boundary layer, the nemesis has it on the tip of the vertical plane, also avoiding the boundary layer of the fuselage. Notice that you put on the table 2 airplanes with propelers, the pitot needs to be far for the properler downwash to avoid interference.

What they measure is the total pressure. Meanwhile the airflow is not disturbed by the boundary layer does not mind is decelerated or accelerated. Is almost impossible to introduce it at undisturbed flow except by setting the pitot in the front of the fuselage

Pitot tubes are often installed at the tail on gliders!

Speed indicator displays IAS(indicated air speed). It has all this position, installation, instrument errors. When you correct for these errors(using tables from aircraft manual) or air data computer you get calibrated air speed(CAS).
Pitot position doesn't matter as it's compensated. High speed low pressure or low speed high pressure. Pressure inside the tube will be the same.

It does not vary. Look at https://en.wikipedia.org/wiki/Position_error and go Pitot system. You can think that position error in this case is compensated. If you get higher pressure you get lower speed. If you have higher speed you have lower pressure... So it doesn't matter where you put Pitot unless it's boundary layer. Boundary layer is effected by other forces like friction so you cannot put Pitot there.

This is a link to the Instrument Pilot handbook offered by the FAA:
http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-15B.pdf
page 97 explains the pitot-static system. It is a simple answer with illustrations. It might not explain every nuance of the system, but it is enough for a pilot to pass his exam!

authors: Асер Мавроди